This invention relates generally to a fast food service technique wherein a meal is first cooked, then refrigerated and stored and subsequently reheated without degrading the basic texture, flavor and nutritional qualities of the meal, and more particularly to a hot-air oven reheating the food.
To meet the growing need for quickly-prepared, low-cost meals, fast-food operations have been developed in which the food to be served is deep-freezed and stored, and when an order is placed for a particular item on the menu, the selected item is withdrawn from the freezer and cooked. In some cases, the frozen meal is pre cooked so that it is only necessary to thaw and reheat the meal.
Though fast food techniques of the type heretofore known make possible relatively inexpensive meals and expedite service, the meals provided thereby are often unappetizing. The reason for this is that while freezing is effective in preserving food and in minimizing contamination, it often does so at the expense of the quality and flavor of the product. In the course of freezing, the moisture content of the food is converted into ice crystals which act destructively; for they rupture the internal structure of the food. As a consequence, frozen food has a characteristically tasteless and mushy quality.
Moreover, in reheating a pre-cooked frozen meal, it is difficult when going from the frozen state to an adequately heated condition to avoid a situation in which the core of the product is still cold even though the outer layer is quite hot. And when one seeks to ensure that the body of the food is hot throughout, there is a tendency to overheat the meal and thereby re-cook it, with a resultant loss of nutritional value and flavor.
A major factor which militates against the success of self-service fast food techniques is that the heated food is necessarily stored in a closed heat chamber which must be opened to obtain access to the product. In a mass feeding operation in which a large number of heated meals must be stored in readiness for withdrawal by customers, this involves a complicated multi-compartment structure, each with. a separate door that must be opened to remove the meal and then closed.
In my above-identified co-pending application, there is disclosed a fast food service technique and apparatus therefor whereby pre-cooked food which has been refrigerated may thereafter be reheated and made directly available to customers without degrading the essential texture, flavor or nutritional qualities of the meal.
In the technique disclosed in my copending application, the food to be served to customers is initially in fresh, uncooked condition. For purposes of illustration, we shall assume that the meal to be served is fish and chips and that the starting ingredients are, therefore, cut pieces of fresh fish and potato slices.
We shall further assume that one hundred meals of fish and chips are to be prepared, each meal to be served in an individual tray of sufficient size to accommodate a full meal. To this end, a sufficient amount of freshly cut fish and potato slices are cooked for one hundred meals. After cooking the cooked products are divided to fill one hundred trays.
It is now necessary to refrigerate the trays to preserve the cooked meals until such time as they are to be served to customers which may be several days later. The trays are kept under refrigeration at a temperature just above their freezing point which, in practice, may be in a range of about 20.degree. to 30.degree. F. Thus where the moisture content of the food is rich in dissolved salts, the freezing point may be well below 32.degree. F. It is important that the refrigeration, while close to freezing, not fall below the freezing point; for the formation of destructive ice crystals in the food must be avoided. It is also important to seal the trays to avoid the loss of moisture and volatile constituents.
Thereafter when the pre-cooked meals are to be dispensed to customers, the trays are taken from the refrigerator and loaded in the open shelves of a heating apparatus Which is adapted to raise the temperature of the meals to a point sufficiently hot to inhibit decay (i.e., above 140.degree. F.) but below the point at which the food would proceed to be recooked. Should some of the meals in the heating apparatus not be consumed in the course of a service period, the sealed trays may be returned to the refrigerator and again cooled preparator to the next demand therefor when they are again heated.
Inasmuch as the refrigeration is at a temperature just above the freezing point, it serves to preserve the food without affecting its quality; and since the subsequent heating of the refrigerated trays maintains the food at a temperature inhibiting spoilage but below the cooking temperature, the heating action is also not injurious. It is possible, therefore, to subject the trays containing pre-cooked meals to more than one cycle of refrigeration and heating without adverse effects.
In the heating apparatus disclosed in my copending application, the refrigerated trays containing pre-cooked food must bc individually loaded into open shelves. The shelves surround a central tube having holes therein, the arrangement being such that heated air is blown through the tube. A portion of the heated air passing through the tube is deflected and forced through the holes to heat the trays in the shelves, the remaining portion of the heated air being diverted to form a heated air curtain about the shelves, thereby isolating the heated trays from the relatively cool ambient air without, however, preventing ready access to shelves to remove heated trays therefrom when they are in condition to be served to customers.
While a heating apparatus of the type disclosed in my copending application overcomes the practical drawbacks of heating ovens which require closed doors to maintain food at the desired temperature level and to prevent heat losses, it has certain practical limitations.
The first limitation is the need to individually load the trays into the heating apparatus, for this is a time-consuming operation. Moreover, since customers must be offered a choice of meals, in order to segregate trays having a meal of one type from trays with a different food content, it is necessary to partition the shelves into separate sectors, each intended for a given type of meal. One must be careful, therefore, when loading the shelves to place the individual trays in the proper sector.
Another limitation resides in the substantial space occupied by the heating apparatus, which, in some instances, rules out its use on a narrow lunchroom counter or other site in which the available space is restricted. Because heated air is forced laterally through spaces between the trays and is deflected thereby, the air emerging from the trays and impinging on the protective curtain is somewhat turbulent and therefore tends to disrupt the curtain. In order to maintain the integrity of the curtain, it must be spaced somewhat from the shelves. This necessarily enlarges the dimensions of the heating apparatus and creates the above-mentioned difficulty.
Yet another limitation of the heating apparatus disclosed in my copending application lies in its inability to quickly raise the temperature of the food in the trays to the proper level. While the heater assembly included in the oven has an adequate capacity to elevate the temperature of the cold food in the trays to the desired level and is thermostatically controllable to maintain this level, the rate at which the temperature can be raised is relatively slow; hence it takes much more than an hour before the food is ready to be served.